State of the art:
I am filing key A. The blank has the right size, but the marks show not well.
Key B: it TURNS! Clockwise, it stops against the bolt. Counterclockwise, it lifts the spring, but cannot throw the bolt. I think the bolt is dirty and rusty. But this means at least that lock B is open already.
Key C: turns but does not reach for the bolt. I suspect, however, that lock C is also already open.
All this means that I have to concentrate on key A…